The present invention relates generally to automotive service equipment designed to measure imbalance in a vehicle wheel assembly, and in particular, to an improved wheel balancer system configured to adjust an imbalance correction threshold level and to check centering of wheels mounted to the wheel balancer system.
Wheel balancer systems are designed to determine characteristics of a rotating body such as a wheel assembly consisting of a wheel rim and a pneumatic tire, or of a wheel rim alone. The determined characteristics include, but are not limited to static imbalances, dynamic imbalances, lateral forces, radial forces and runout parameters. Determination of some of these characteristics result from direct measurements, while others are obtained from an analysis of the mechanical vibrations caused by rotational movement of the rotating body. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers mounted in the wheel balancer system, which are configured to convert the mechanical vibrations into electrical signals.
Existing wheel balancer systems suffer from subtle deficiencies in connection with providing compensation for run-out and in tire to rim matching procedures. These systems, such as the GSP9700 Series manufactured by Hunter Engineering Co. of Bridgeton, Mo. are capable of displaying an angular location at which a pneumatic tire should be mounted to a wheel rim to minimize an overall radial force variation associated with the wheel assembly. For an accurate measurement of rim runout at the beadseat of the tire, it is necessary for the rim runout to be measured without the tire mounted thereon, and then for the rim to be dismounted from the balancer, and the tire mounted to the rim. The wheel assembly consisting of the tire and rim is then remounted to the balancer to measure the force variations associated therewith. Any centering difference with respect to the initial and subsequent mounting of the rim and wheel assembly on the balancer spindle will result in errors in the determination of the rim runout, the assembly force variation, and the tire force variation computations. This “centering error” can become even more significant with larger wheel assembles, such as those currently entering the market.
There are many types of adaptors for use when mounting and centering wheels onto a balancer spindle. Common examples of adaptors are cones, centering sleeves, flange plates with rigid pins, flange plates with compliant pins, clamp cups and other devices as can be seen in publications such as Hunter Engineering Company accessory brochure, Form No. 3203T, entitled “Wheel Balancer Accessories”. Often there are several different adaptors that may be used to mount a wheel on a wheel balancer. Due to variations in wheel design there are usually several adaptors, or combinations of adaptors, that appear to fit the wheel, but actually do not center the wheel adequately on the wheel balancer shaft. Accordingly, it is desired to develop a solution to aid the operator in selecting the best adaptor for a wheel.
One solution to the centering error problem induced by the dismounting and remount of a wheel rim or wheel assembly on a balancer system spindle is addressed in U.S. Pat. No. 6,481,282 B2 for “Wheel Balancer System With Centering Check”. The solution set forth in the '282 patent requires that the wheel rim runout be measured before and after the wheel rim is dismounted from the balancer system, and a comparison carried out. If the comparison of the two runout measurements indicates a difference which is greater than a predetermined threshold, it is assumed that the wheel rim has not been properly centered on the balancer spindle during the remounting procedure, and a warning is provided to the operator. The solution presented in the '282 patent further requires that the wheel balancer system include the capacity to measure and store wheel rim runout parameters (i.e. magnitude and phase) for subsequent comparisons with predetermined threshold values.
As not all wheel balancer systems are capable of measuring wheel rim runout, it would be a particular advantage for a wheel balancer system to incorporate a centering check process which does not require a measurement of wheel rim runout both before and after altering the balancer mounting of the of a wheel rim or wheel assembly.
While accurate centering of a wheel rim or wheel assembly on a balancer is important to obtain accurate measurements of any imbalance present therein, it is additionally important to provide an operator with information about whether or not there is a need to correct a detected imbalance in the wheel rim or wheel assembly, or if the detected imbalance is sufficiently small so as to have a negligible effect on vehicle performance and handling. Currently, wheel rim sizes in the U.S. market range from 13.0 inches in diameter up to and including the present DOT limit of 24.0 inches in diameter. It is anticipated that wheel rim sizes will increase to 26.0 inches in diameter in the near future, with a corresponding increase in associated tire sizes. A problem presented by the continued increase in wheel rim and wheel assembly sizes is the effect of a fixed imbalance correction threshold level.
Due to the limited size increments in which imbalance correction weights are available, conventional balancer systems are configured to display as zero any required imbalance correction weight values below a predetermined threshold. Typically the predetermined threshold is 0.29 oz., and is selected to be slightly greater than the smallest imbalance correction weight increment, regardless of the size of the wheel rim or wheel assembly. This can result in an operator “chasing” weights on a small or narrow wheel due to the significant effect of the threshold level on imbalances, and a poor balance on larger diameter wheels due to a reduced effectiveness of the threshold level. One solution is shown in U.S. Pat. No. 6,484,574 to Douglas, in which a balancer is configured to select the best weight plane locations from data acquired by scanning the rim profile. This is an advantageous method, but it is not economical for all balancers to have this feature.
Clearly, it would be further advantageous to provide a wheel balancer system with a method for determining an imbalance correction threshold level which varies in relation to the dimensions of the wheel assembly undergoing balancing in addition to the incremental size of the imbalance correction weight employed, and which provides an operator with a scaled visual indication of any remaining imbalances present after application of suggested imbalance correction weights at suggested weight placement locations.